A radar altimeter is an aircraft sensor that measures altitude above terrain by transmitting a radio signal and receiving a reflection of the signal from a terrain surface. The radar altimeter measured altitude is an important piece of information used by a pilot and onboard systems (e.g., an autopilot system) during the various phases of flight, including approach and landing.
Currently, an aircraft is usually equipped with several radar altimeters. Typically, the measurements from all radar altimeters are processed (e.g., compared to each other) and the resulting value of the altitude is provided to onboard systems and the pilot. However, the altitude is provided without any information related to its accuracy or integrity, which limits utilization of radar altimeter measurements in envisioned applications related to more autonomous aircraft.
Accuracy and integrity of the navigation information (horizontal and vertical position) provided by a Global Navigation Satellite System (GNSS) based navigation system or hybridized Global Navigation Satellite System and Inertial Navigation System (GNSS/INS) based navigation system with respect to possible faults of GNSS satellites has been solved since the advent of GNSS-based navigation systems. However, accuracy and integrity of the navigation information provided by a navigation system utilizing radar altimeters with respect to possible faults of the radar altimeter has not been addressed yet.